1. Field of the Invention
The present invention relates to a projection type image display apparatus which uses a small-sized ferroelectric liquid display device, and projects, under magnification with a high contrast by using a projection lens, image information carried by a luminous flux emitted from the ferroelectric liquid display device.
2. Description of the Prior Art
Various kinds of projection type image display apparatus by which a luminous flux carrying image information emitted from a liquid crystal display device is projected onto a screen under magnification by way of a projection lens have recently been known, and attention has been focused on those using a reflection type liquid crystal display device as their liquid crystal display device.
Meanwhile, an apparatus shown in FIG. 2 has been known as a projection type image display apparatus which projects a color image by using reflection type liquid display devices.
As shown in FIG. 2, by way of a polarization beam splitter (hereinafter referred to as PBS) 31, S-polarized light acting as illumination light enters a three-color-decomposing/combining prism 36, by which it is decomposed into three color light components of R, G, and B. The color light components are made incident on their corresponding reflection type liquid display devices 32A to 32C and are modulated in response to respective image input signals to the devices 32A to 32C. This modulation is effected such that pixels are turned ON in areas having a higher luminance (white image areas) but are turned OFF in areas having a lower luminance (black image areas). Luminous fluxes reflected by ON-state pixels are converted into P-polarized light, which then pass through the PBS 31, so as to be projected onto a screen by way of a projection lens 33. For enhancing the contrast of projected images, an analyzer 34 is inserted immediately in front of the projection lens.
When the light transmitted through the PBS 31 reaches the projection lens 33, it is reflected by each lens surface though with a very low intensity and, in a predetermined projection environment, may be re-reflected by the reflection type image display devices, so as to reach the screen. Namely, it may become stray light (ghost), thereby lowering the contrast.
As an apparatus which can improve the contrast on the screen in such a case 1 the technique disclosed in Japanese Unexamined Patent Publication No. 8-271855 has been known. It uses the configuration shown in FIG. 2 as a basic configuration, and inserts a quarter-wave plate 35 between the projection lens and the image display devices in order to improve the contrast.
The technique disclosed in the above-mentioned publication uses three image display devices and employs the color-decomposing/combining prism in addition to the polarization beam splitter, thereby increasing its weight and cost. While there has recently been a strong demand for reducing the weight and cost of the projection type image display apparatus, no dramatic improvement can be expected as long as the configuration of the above-mentioned prior art is employed. Reducing the number of image display devices is effective in terms of cost, whereas reducing the number of optical components (such as glass components like prisms) is effective in terms of weight.